Recent genetic work suggests that the genus Stenella is paraphyletic, and it is likely that the Delphininae will be restructured in coming years (LeDuc et al. 1999). Two subspecies are recognized: S. a. attenuata in oceanic tropical waters world-wide, and S. a. graffmani in the coastal waters of the eastern tropical Pacific (ETP) (Perrin 2002).

Justification:
The abundance estimates available total more than 2.5 million, and additional likely large populations in the Atlantic, Indian and Pacific Oceans have not been assessed. The northeastern population in the ETP declined 76% within the last three generations (69 years), but that decline has ceased and was not large enough to constitute a global decline of 30%. Large impacts of direct catch and bycatch in other regions have not been identified, and it is unlikely that the global population has been reduced by as much as 30%. Therefore, the species is assessed as Least Concern.

Stenella attenuata attenuata is pantropical, found in all oceans between about 40°N and 40°S, although it is much more abundant in the lower-latitude portions of its range. The range extends to some enclosed seas, such as the Red Sea and Persian Gulf, but does not include the Mediterranean Sea (Perrin 2001, 2002).

Stenella attenuata graffmani – the coastal Spotted Dolphin is found only in a narrow band (<200 km wide) along the coast of Latin America, from southern Mexico to Peru (Perrin 2001; Escorza-Treviño et al. 2005). Recent genetic data suggest there may be several populations contained within this subspecies (Escorza-Treviño et al. 2005).

The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.

In the eastern Pacific, there were an estimated 228,038 coastal Spotted Dolphins in 2000 (CV=34%; Gerrodette and Forcada 2002a). The north-eastern offshore Spotted Dolphin (the form most affected by the ETP tuna fishery) numbered about 737,000 in 2003 (CV=15%; Gerrodette et al. 2005), a reduction of 76% from original size in 1959 (Reilly et al. 2005). This population is not showing clear signs of recovery despite the dramatic decline in mortality in recent years (Gerrodette and Forcada 2005). The western/southern offshore stock (which is less affected by the fishery) numbered about 876,075 in 2000 (CV=31%; Gerrodette and Forcada 2002b). In Hawaiian waters, there are an estimated 8,978 (CV=48%) (Barlow 2006). About 438,000 inhabited Japanese waters in the early 1990s (Miyashita 1993). There are estimated to be 34,067 (CV=18%) in the northern Gulf of Mexico (Mullin 2006), and 4,439 (CV=49%) along the east coast of the United States (Waring et al. 2006). Dolar et al (2006) estimated about 14,930 (CV=41%) for the eastern Sulu Sea and 640 (CV=27%) for the Tañon Strait between the islands of Negros and Cebu.

In the eastern Pacific the Pantropical Spotted Dolphin is an inhabitant of the tropical, equatorial and southern subtropical water masses. The waters in which the animal occurs with greatest frequency are those underlain by a sharp thermocline at depths of less than 50 m and with surface temperatures over 25°C and salinities less than 34 parts per thousand. These conditions prevail year round in the region north of the Equator called the "Inner Tropical" waters of the eastern Pacific. Occurrence in this core habitat is correlated with apparent multi-species foraging and feeding behaviour. The species also occurs in similar waters south of the Equator that expand and contract greatly with season and year to year (Perrin and Hohn 1994). In the Atlantic, S. attenuata is primarily a dolphin of the high seas and oceanic islands, but in the eastern Pacific a large-bodied subspecies occurs along the coast from Mexico to Peru. Detailed analysis of oceanographic correlates of distribution will be necessary in order to understand fully the habitat requirements of these pelagic dolphins, often the most conspicuous elements of tropical cetacean communities around the world (Ballance and Pitman 1998).

Offshore Spotted Dolphins feed largely on small epi- and mesopelagic fishes, squids, and crustaceans that associate with the deep scattering layer (Robertson and Chivers 1997). In some areas, flying fish are also important prey. The diet of the coastal form is poorly known, but is thought to consist mainly of larger fishes, perhaps mainly bottom-living species (Perrin 2001, 2002).

Offshore Spotted Dolphins bore the brunt of the massive dolphin kill by tuna seiners from the late 1950s to the 1980s in the eastern Pacific (although the coastal subspecies was also impacted). For example, in the period 1959 to 1972, nearly five million dolphins were killed, and of this number, about three million were from the north-eastern offshore population (Wade 1995). Since the Inter-American Tropical Tuna Commission (IATTC) implemented per-vessel mortality limits on the international fleet, the combined annual mortality for all Spotted Dolphins in the ETP has decreased greatly, e.g. to only 373 in 2005 (IATTC 2006). Although current mortality is greatly reduced, the north-eastern form appears to be recovering very slowly, if at all, and potential factors such as fishery-related stress, unobserved mortality due to calf separation and orphaning during fishing operations (Archer et al. 2001), possible mortality by small vessels that do not carry observers, under-reporting of mortality, and ecosystem change, have been suggested as possible reasons for the species’ slow recovery (Gerrodette and Forcada 2005).

Spotted Dolphins are also taken incidentally in local fisheries along the Central American coast (Palacios and Gerrodette 1996).

Yang et al. (1999) also reported incidental mortality in Chinese fisheries, and Dolar 1994 found incidental spotted dolphin takes in the Philippines. An unknown but suspected large number of Pantropical Spotted Dolphins are taken by the large-mesh pelagic driftnet fishery off eastern Taiwan (J. Wang pers. comm.).

Japan takes large numbers of spotted dolphins for human consumption. The catch in 1982 was 3,799, and annual catches between 1994 and 1997 ranged from 23 to 449 (Perrin 2002). Between 1995 and 2004, the average annual catch was 129 animals (Kasuya 2007). The drive fishery for Spotted Dolphins began in 1959 and is thought to have caused a slight decline in the minimum age at attainment of sexual maturity in females (Kasuya 1985).

Pantropical Spotted Dolphins are also taken in hand-harpoon fisheries in the Philippines (Dolar et al. 1994); in Taiwan, where it is the locally preferred species of cetacean for human consumption (J. Wang pers. comm.); and regularly or opportunistically by gillnet and harpoon in India and Sri Lanka (Perrin and Hohn 1994). Drive hunts at Malaita in the Solomon Islands took several hundred or thousands of Spotted Dolphins annually in the 1960s; the hunts continue at present (Ross et al. 2003, Kahn 2006). Small numbers are taken in numerous small subsistence fisheries for dolphins and whales around the world, e.g. at St. Vincent in the Lesser Antilles (Perrin and Hohn 1994) and Lamalera in Indonesia (Kahn 2004). Most of these kills have not been adequately monitored and the effects on the subpopulations are usually not known.

Dolphins and small whales of several species, including S. attenuata, putatively interfere in hook-and-line fisheries for squid and yellowtail in the Iki Island region of Japan (Kishiro and Kasuya 1993). Bounties have been paid to fishermen for dolphins killed since 1957. During the period 1976–1982 a total of 538 Spotted Dolphins were killed. The effect of these takes on the regional population is not known (Perrin and Hohn 1994).

Spotted Dolphins, as with other species impacted by the ETP tuna purse-seine fishery, are managed both nationally by the coastal countries and internationally by the IATTC. The IATTC has imposed annual stock mortality limits on each purse seine and promulgated regulations regarding the safe release of dolphins (Bayliff 2001).

As the species comprises several subspecies and regional populations, the conservation status of each of these should be assessed separately since the available estimates of abundance and removals suggest that some of them may fall into a Threatened category.

Dolar, M. L. L. 1994. Incidental takes of small cetaceans in fisheries in Palawan, Central Visayas and northern Mindanao in the Philippines. Reports of the International Whaling Commission 15: 355-363.